Our initial objective is to evaluate the potential of hyperthermia as a radiosensitizer for a rapidly proliferating normal murine tissue (duodenal crypt lining epithelium), a slowly-turning-over normal murine tissue (spinal cord) as well as a slow-growing (Slow Line) and a fast-growing (S102F Line) C3H mouse mammary tumor. Hopefully, this combination of tissues will allow us to assess the hyperthermic radiosensitization for both the early and late effects on normal tissues and on tumors with dramatically different growth kinetics. The hyperthermia will be induced locally via a 915 MHz microwave system and the effects on the various tissues will be assayed respectively by microcolony crypt survival, hind-leg dysfunction, tumor growth delay and local tumor control (TCD50/120). Several temperatures and heating intervals will be studied as will heating both before and after x-irradiation. The therapeutic indices for tumor versus normal tissues will be determined for the various protocols. Our long-term goal is to gain additional insights into the feasibility of introducing hyperthermia as an adjuvant for clinical radiation therapy.